The present invention relates to a message guaranty system and, more particularly, to a message guaranty system capable of guaranteeing that messages have indeed been transmitted and received between terminals connected on a network system.
A number of conventional methods exist for guaranteeing the transmission and reception of messages between workstations connected on a network system. One such method involves having the transmitting and receiving workstations each manage a message start serial number and a message end serial number which are assigned to each message sent from one side to the other. Another method requires establishing a sequence in which the receiving workstation returns an acknowledgement in response to each message received from the transmitting workstation.
More specifically, the former conventional method (of managing message serial numbers) requires that four serial numbers, i.e., the message start and message end serial assigned to each of the transmitting and receiving terminals, coincide with one another before transmission or reception of any message. When the transmitting terminal transmits the message, the receiving terminal increments its message start serial number by 1. With the message received, the receiving terminal increments its message start serial number by 1. The receiving terminal then processes the message. With the message processing completed, the receiving terminal increments its message end serial number by 1 and returns an acknowledgement message to the transmitting terminal. Having received the acknowledgment message, the transmitting terminal increments its message end serial number by 1. This terminates the entire processing of message transmission/reception. This kind of message serial number management is carried out under the NIF/OSI (Network Interface Feature/Open Systems Interconnection) protocol. If there occurs a serial number mismatch between the transmitting and the receiving terminal, an error is suspected to have occurred in the message processing.
The latter conventional method (of establishing an acknowledgement sequence) requires that the receiving terminal must always return an acknowledgement message (ACK) in response to the message sent from the transmitting terminal. The return of the ACK message is supposed to guarantee an error-free message transmission.
A further method is proposed by Japanese Patent Laid-open No. Hei 4-227154 (cited reference 1). The proposed method involves furnishing a securely managed encryption key and a powerful encryption algorithm whereby the transmitting terminal furnishes the target message with a token constituting a collection of specific information. Using the same encryption key and algorithm, the receiving terminal prepares an authentication token (a collection of information for authentication purposes) by which the token of the received message is checked for authenticity. If any dispute occurs between the transmitting and receiving parties regarding the transmission or reception of a particular message, the two parties alone are responsible for resolving it.
The above conventional methods are effective in detecting mismatches in message processing but fail to provide for eventualities in which the transmitting or receiving party denies having transmitted or received a specific message. Although the system of the cited reference 1 provides high degrees of message authentication, the fact that any dispute is left to be resolved not by any reliable third party but only by the parties concerned does not make the system suitable for an open, distributed environment.